657 
38 F8 
3PV 2 



[TRANSACTIONS ,0F THE AMERICAN INSTITUTE OF MINING ENGINEERS. 



Notes On the Northern Black Hills of South Dakota. 

BY PERSIPOR PRAZER, PHILADELPHIA. 

; (Chicago Meeting, February, 1S97.) 

General Geology of the Northern Black Hills. 

The " Black Hills of Dakota," to the northern part of which 
the following observations apply, occupy a position on cither 
side of the boundary between Wyoming and South Dakota, 
approximately between 103° 15' and 104° 48' of west longi- 
tude and 43° 15' to 43° 50' of north latitude. The area is 
roughly 4160 square miles.* (See Plate I.) 

As has been pointed out by Profs. H. O. Hofman, F. W. 
Carpenter and others, and illustrated by Mr. Newton in the 
publications of the United States Geological Survey, these hills 
are made up of a large number of the known formations from 
the Archean to the Tertiary, which latter constitutes the bor- 
der of the region. The mining operations are largely contined 
to the interior of this area, and the centers from which they are 
conducted (Deadwood, Lead City, Galena, etc.) are situated 
near the line of junction of the Archean schists and quartzite, 
supposed to represent the Potsdam Sandstone of the N. Y. 
series, or the lowest of the Paleozoic measures. 

The Archean or pre-Paleozoic rocks consist maiidy of a 
mica-schist in which hornblende and garnet are frequently 

* There are many of my fellow-members to whom the aspect of the Black Hills 
and the adjacent Bad Lands is familiar— in the more genial montlis of late 
spring, summer, and early fall ; but to these, even, the conditions surrounding 
this lately re-exploited country in the middle of winter are unknown. Very 
lately it became necessa-ry for me to undertake a visit of exploration to the Dead- 
wood district while the thermometer was registering — 42° Fahrenheit, and the 
high winds prevailing in early December of 1896 were creating havoc with those 
settlers who were imprudent enough to brave the elements without sufficient pro- 
tection, or who had not adequately housed their stock. 

By singular good luck the blizzard and I crossed each other en route, and I found 
in Northern South Dakota one of the most delightful winter-temperatures I have 
ever known. 

1 



"/ 



2 NOTES ON THE NORTHERN BLACK HILLs'oF SOUTH DAKOTA. 

found, but which varies in texture and composition so as to re- 
semble not infrequently the hydro-mica schists or " nacrites " 
of the late Dr. T. Sterry Hunt, and again to assume the appear- 
ance, and in part the constitution, of heavy bedded gneiss. 
These schists are upturned at high, often vertical angles, while 
over them unconformably, and dipping gently towards the 
horizon is the quartzite in its various forms ; sometimes appar- 
ently undisturbed, and at others broken or " brecciated," as it 
is often called (/.c,, shattered into angular fragments and re- 
cemented without very great displacement of the parts) by the 
numerous porphyry dikes Avhich intersect all the exposed 
measures from the lowest to the highest, and form a part of 
the elevations or hills of the region. These latter are without 
question eruptive, and bear evidence of having been ejected 
during at least two and probably several diiierent epochs, for I 
have observed porphyry in places intersecting older masses of 
similar porphyry, which, in their turn, have produced earlier 
disturbances in the strata. 

The same paper contains a geological section taken from the 
equally admirable and earlier contribution of Walter B. Dev- 
ereux, on " The Occurrence of Gold in the Potsdam Forma- 
tion, Black Hills, Dakota " {Trans., x. 465). 

The first systematic study of this region was made by Dr. 
F. V. Hayden, in 1870, and resulted in the geological definition 
of the large divisions of the Hills much as they are accepted 
to-day. 

Since then the Government has had the very full report on 
the geology and resources of the Black Hills by Henry Newton 
and W. P. Jenney, 1875 (Report published in 1880). Still 
later Devereux, Blake, Headden, Ilofman, Carpenter, liickard, 
Farrish, Dr. McGillicuddy and others have published valuable 
contributions to our knowledge of the geology, mineral re- 
sources and chemical character of the ores of the Black Hills, 
which will be referred to more specifically in their proper 
places. Plate I., accompanying this paper, is a reproduction in 
black and white of the geological map published with the ad- 
mirable paper of Prof. F. B. Carpenter {Trans., xvii., 598) on 
" The Ore-Deposits of the Black Hills." 

The district which is my present subject, lies in that part of 
the northern Black Hills immediately around Galena and three 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA, 3 

miles west and three miles southwest of that camp, which is 
some six miles southeast of Deaclwood in an air-line. 



Plate I. 



Longitude West from Greenwich ' 103 




mHH Igneous 

I ] T..t.u. 

j r^.;;.J..| Jura-Trias 



p, ^ j Caiboniferous 

['^'Sf^^^i Cambrian 
I t Archsau 

Granite 



Scale of Miles 
5 10 



Geological Map of the 

BLACK HILLS OF DAKOTA 

After the Map of Henry Newton, E.M. 
By Franklin R. Carpenter, Ph.D. 



4 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

According to the topographical sheet of the United States 
Geological Survey (DeadWood, S. D., Ed. of Feb., 1894), the 
town of Galena lies on the 4800-foot contour-curve above tide. 
The hills along Bear Butte creek rise to 5200 and 5300 feet, 
making their summits 400 to 500 feet above the creek. To 
the northwest, or between Galena and Deadwood, and to the 
southwest, near the intersection of Bear Butte and Strawberry 
gulches, the extreme summits reach 5500 feet. 

The numerous gulches follow many directions; but those 
which predominate are approximately northeast-southwest and 
northwest-southeast. The valleys are generally deep and the 
hillsides steep, indicating a considerable erosive action of the 
streams on the sides, and accounting for the numerous placer- 
deposits found in their beds. 

The geology of the region, if not simple, is at least not com- 
plicated by a large number of formations. 

The mica-schists, thought to be upper members of the 
Archean, are found at the lowest levels along the streams and 
higher up on the hills, as at the Cora mine, striking northeast- 
southwest, and dipping at angles from 38° to 85°. 

These schists are generally micaceous and coarse-grained and 
usually rather reddish from the dissemination among them of 
iron oxides ; but they vary greatly, sometimes passing into the 
type known as nacrite or hydro-mica schist (which here also 
has been frequently but incorrectly taken for talc schist) and 
sometimes, though more rarely, assuming a heavy bedded- 
character reminding one of gneiss. 

They are most frequently crumpled and conchoidal both in 
small and in large bed planes. 

Explorers. — Hayden reported the Black Hills of Dakota as 
one of the plainest and most interesting exhibits of the series 
from the granite upwards, of all localities known in the West.* 

E'ewton and Jenney issued a most instructive volume, f and 
one which has served as a mine for all future observers. The 
map accompanying this work is that generally used for all pur- 
poses of geological illustration of the region to-day. 

* Meek and Hayden : " Some Eemarks on the Geology of the Black Hills and 
Portions of the Surrounding Country," Proc. Acad. Nat. ScL, Phila., vol. x., pp. 
41-49, 1859. 

t "Geology of the Black Hills and Mineral Resources of the Black Hills of 
Dakota," U.S. Oeol. Survey, 1880. 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 5 

Walter B. Devereux* thought that the oldest visible forma- 
tions near Deadwood were pahieozoic schists (?) 

Resting unconformably upon them was a sedimentary forma- 
tion composed of debris derived from them, i.e., the Potsdam. 
The lowest is a conglomerate. The mines in the lower part of 
the quartzite are called cement-mines. The deposits were found 
on the east side of the Homestake vein. Only one deposit was 
worked on the western side. 

The mass of the conglomerates was a mixture of quartz 
boulders, pebbles and schist, with pebbles of hematite ; gold 
was present as a mechanical, and in the cement-beds as a 
chemical, constituent. In general only 5 or 6 feet of rock will 
pay for mining or milling. Cutting through a dike, he found 
that gold was seldom present in close proximity to the por- 
phyry. Gold plates are found along the interior plane of the 
" talc " (?) schist. The schists underlying this deposit were 
found to contain gold for about 10 feet. The ores of Bald 
mountain seem to be impregnations. 

1. The metallic constituents were segregated along certain 
horizontal strata. 2. There was concentration along certain ver- 
tical planes which were contacts of quartzite with porphyry 
dikes. The dikes themselves were found to be lines of mineral 
segregation below the contact of quartzite and of the schist. 
He inclined to the belief that the gold came partly from below 
and partly from the concentrated sediments above. 

In one place the sedimentary stratum gave $20 per ton in 
gold, though £0 fine that no gold could be panned. 

Argentiferous lead-ores have been mined from the quartzite. 
These mineralizations j^robably are of the age of the porphyry. 

Dr. Headdenf thought that the strike of the granites was the 
same as the schists with which they are interstratified. The 
granites further north are more Varied. It is a question 
whether they are continuous undeground. On the eastern 
margin of the schists occur lenses, some large and some small, 
with their longer axes parallel. Many of the granites are in- 
trusive. There is no porphyry in the southern section of the 
Hills. 

* Op. cit., Trans., x., 465, May, 1881. 

t "Notes on the Hist., etc., of the Black Hills," by Dr. W. P. Headden, Proc. 
Colo. Sc. Soc, vol. iii., pt. 3, p. 347. 



6 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

The Cambrian is unconformable on the schists, part of which 
form its basal conglomerate. 

Prof. Hofman* says that the gold is found in quartzite and 
pyrite finely divided through mica- and amphibole-schists, and 
impregnates the schists. Its associated minerals are pyrite, 
with some arseuopyrite, chalcopyrite, garnet, and asbestos. 
The ores from the upper cuts and levels are more free-milling 
than those below the water-line. The assay-value of pure con- 
centrates is $4 to |90 per ton ; the average perhaps $25 per 
ton. The porphyry forms barren horses. 

From the valuable contribution to this subject made by Prof. 
Carpenterf I have compiled the following summary : 

The Cambrian is represented only by the Potsdam and rests unconformably on 
the Archean scliists. No Silurian or Devonian is found, and the Potsdam and 
Carboniferous are conformable. The great deposits are of Archean age and yield 
mainly auriferous pyrite. There are sometimes lenticular and seemingly inde- 
pendent masses of the slate and schist series sharing the folds and contortions and 
having a columnar cleavage coincident with the bedding. The porphyry flowed . 
over the Potsdam east of Dead wood and under that in the Homestake to the west, 
lifting it like a laccolite. The gold was deposited by chemical action after having 
been segregated. 

The smaller the particles the finer the gold (Devereux). 

Assays of Homestake porphyry show that it contains no gold. Tlie wliole 
thickness of the beds in which these ore-bodies occur is about 2000 feet. 

The ore-bearing rocks are co-extensive with the igneous rocks. 

The Potsdam ores occur at different levels, especially in the upper parts of the 
lower quartzite. Bluish quartzite contains very finely divided pyrite in a silice- 
ous paste, which unites the rounded grains of silica. The solutions which brought 
this material to fill the spaces between the grains brought also the silver and gold. 
At Galena the proportion of gold is greater in the lower contact, while silver pre- 
dominates in the upper, which are the more calcareous parts of the Potsdam. In 
the limestone the deposits carry lead and silver ; but the porphyry is the same. 
The solutions followed certain bed-planes which are on the quartzite and in the 
lime-shales of the Potsdam. The connection between the overlying porphyry and 
the ore is intimate. Where one is wanting, so also is the other. The crystalline 
schists below have nearly always shown gold. Perhaps the porphyry only in- 
duced hot waters which dissolved and redistributed it. The slates below the Pots- 
dam at Galena show galenite also (in the Oro Fino mine). Blende, galenite and 
pyrite occur in the porphyry. 

At Galena there are three distinct ''contacts" or levels of ore, always on 
quartzite, on which it is found replacing parts of the thin lime shales, and over 
it, though not always in contact, is porphyry. 

No ore-bodies have been found to pass from the porphyry into the Archean. 



* "Gold-Milling in the Black Hills," by H. O. Hofman, Trans., xvii., 498, 
Feb., 1889. 

t Op. cit., Trans., xvii., 570, Feb., 1889. 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 7 

The outcrop of the Galena deposits is almost always lead and iron carbonates car- 
rying silver. The depth at which these become sulphides varies with the po- 
sition of the deposit ; in tlie lower contact, quickly ; in upper contacts, they con- 
tinue to greater depth. 

The "veins of granite" of Newton, Jenney, Blake, and Vincent are segre- 
gated parallel to the apparent bedding. They are lens-shaped and succeed each 
other in strike, and probably also in dip. They are tabular in form (?) When tin 
is present, one of the constituents of the granite is wanting, and the rock becomes 
quartz and mica, or quartz, feldspar and mica. 

The quartzite which is tlie main locus of the ores lies unconformably upon these 
schists, not deviating more than 20°, but usually presenting the appearance of be- 
ing in general nearly horizontal. This quartzite is sometimes banded, and so 
compact as scarcely to differ from a quartz-vein aspect ; but usually it is of com- 
paratively uniform light color, interspersed here and there with small crystals of 
pyrite and arsenopyrite, and, in the region under discussion, much broken from 
the intrusion of numerous dikes of porphyry. 

Galena, zincblende, arsenopyrite and other accessory minerals are found on the 
fracture-planes of the quartzite, and to a certain extent within its mass near to 
these planes. There are three levels of the quartzite rock in what has been taken 
for the Potsdam formation, and there is evidence of quartzite horizons. 

In general it may be said that the alteration of the original sandstone to quartz- 
ite is more complete in the lower than in the higher horizons, and that the high- 
est of these siliceous members of the Potsdam is capped by a series of shales or 
" lime-shales." 

The topography of the Galena region has already been stated 
in general terms. (See Plate II.) It consists of a network of nar- 
row and deep gulches separated by steep hills whose shoulders 
are about 300 feet, and whose crests are 500 feet above water- 
level. It is more than probable that the directions of these 
narrow valleys in many instances indicate the directions of por- 
phyry outflows between the broken quartzite and shale, since 
the decomposed porphyry is the most easily eroded of all the 
rocks in the region, and would offer the least resistance to the 
wearing action of running water. Still, other causes were 
potent in modeling the hills as we now see them, among 
which a very important one must have been the agency of 
moving ice. However this may be, the steep portions of the 
hills up to the shoulders just spoken of are largely composed of 
quartzite. The summits, in those localities where the por- 
phyry lias overflowed, show by their gentle slopes the charac- 
teristic moalding of weathered porphyry ; but in other localities 
a difterent contour is noticeable, characteristic of the almost 
equally soft " lime shales." It is important to keep in mind this 
general distribution of the porphyry, and especially so when 
considering the Union Hill mining properties (See Plate III.), 



8 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

because the Hill is largely composed of porphyry, and, from 
the state of the gold which it contains, constitutes a valuable 
ore. The earlier geologists who examined the Black Hills were 



Plate II. 




GALENA DISTRICT, SOUTH DAKOTA. 

(Redvced/rom Dtadwood Sheet U.S.G.S.) 

Scale of Miles 

1012345 

I 1 1 J I I J 



of the opinion that this rock was barren of valuable metals. 
Thus Devereux reported that about 5 or G feet of the quartzite 
would pay for mining and milling, and that " gold was seldom 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 



present in close proximity to the porphyry." He thought that 
the planes of contact, fracture and bedding were enriched, and 
that 10 feet or so of the schists below the quartzite (the schists 
underlying the Potsdam) contained gold. The Bald mountain 



^y;^/' Base Line ^of-hev^\fj^'^> 



Plate III. 
GALENA DISTRICT, 

LAWRENCE COUNTY, 
SOUTH DAKOTA. 

SCACE OF FEET 



HouseVElMvation 1C4 




CLARES 



deposit he regarded as an impregnation. Carpenter believed 
that the Homestake porphyry contained no gold, but that the 
thickness of the beds in which ore-bodies occur was 2000 
feet, and that the ore-bearing rocks were co-extensive with the 
igneous rocks. He was of the opinion also that the solutions 
which brought the finely-divided pyrites to fill the spaces be- 
tween the grains, brought silver and gold ; that the connection 



10 NOTES ON THE NORTHERN BLACK HILLS OP SOUTH DAKOTA. 

with the porphyry was intimate in the Galena region ; but that, 
perhaps, the porphyry only induced the hot waters which dis- 
solved and redistributed the gold. 

Blende, galenite and pyrite, he says, occur also in the por- 
phyry, but no ore-bodies have been found to pass from the porphyry 
into the Archean. 

Prof. Ilofman mentions the quartzite and schists as carriers 
of gold, but describes the porphyry as forming " barren 
horses." 

^Nevertheless, subsequent tests of at least a part of the por- 
phyry outflows show that, to some extent, free-milling gold is 
carried in this rock, and on account of its enormous extent and 
the ease and economy with which it can be mined, it is im- 
portant to determine its richer zones. To this end a number 
of openings have been made on the surface of Union Hill. A 
shaft nearly 300 feet deep to the bottom of the sump has been 
sunk, and a tunnel of 359 feet E".W. from mouth to heading has 
been run, with a cross-cut 123 feet E. of E"., begun from a point 
227 feet from the mouth of the main tunnel. 

Starting at a cabin stable on Strawberry creek, near Mr. Fa- 
gan's house, I ascended the hill in an easterly direction, taking 
carefully-averaged samples from a pit at the base of the hill. 
The material is a weathered porphyry and the pit about 10 feet 
deep (nearly filled with snow at the time of my visit). Between , 
this pit and the open cut, about 150 feet IST.E. and considerably 
liigher, nothing was observed on the surface but porphyry in 
various stages of decomposition. The rock in which it is exca- 
vated is also a rotten porphyry, of which large masses are ex- 
posed. In this cut a small natural bridge of rock has been left 
standing. 

About 50 feet west of this cut is another, also in decayed 
porphyry, in which the principle cleavage-planes dip more or 
less westerly. Both the last-mentioned openings are near the 
shaft-house at the top of the hill. 

The shaft-house covers a shaft 280 feet deep, with a sump of 
about 20 feet below the second level. At the time of my visit 
the lower level was inaccessible, and I visited only the first, or 
140-foot, level, from which two drifts had been started, one ex- 
tending 30 feet S.E. and the other 40 feet N.W. of the shaft. 

At the breast of the S.E. drift a " horse " of" barren quartzitic 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 11 

rock" had come in at tlie roof, inclining E. about 45°, and ap- 
parently of lenticular shape. 

The porphyry in the N.W. drift is remarkable for being very 
full of disseminated pyrite. It is said to be the only instance 
of the kind thus far found in the Union Hill shaft. 

In a cut near the shaft-house a loose mass of quartzite was 
observed, lying in porphyry. 

Renewing the examination of the surface of the hill from the 
top of the shaft, I visited a cut in white porphyry about 700 feet 
east by south of the latter and obtained samples for analysis. 
An experimental shaft in porphyry, about 200 feet S. 10° E. of 
the last and 180 feet lower, also furnished samples which were 
analyzed, A winding open cut in rock, similar to that which 
has been above described, about 50 feet long, about 250 feet 
south of the last point, and said to be about 50 feet above the 
floor of the main Hoodoo tunnel, was examined and sampled. 
Finally, a short tunnel in rotten porphyry, with apparently 
horizontal cleavage-planes, about 150 feet W. 20° N. of the 
mouth of the main Hoodoo tunnel, yielded its quota to the ma- 
terial collected for investigation. 

About 150 feet E. 20° S. from this cut is the mouth of the 
Hoodoo tunnel proper. The opening of this tunnel is in por- 
phyry like that of the other openings described, but with planes 
of cleavage (thought by some to correspond to the stratification 
of the disturbed quartzite), dipping SE. 20°. These planes are 
also noticeable in the upper and shorter tunnel. 

This rotten porphyry extends inward for about 60 feet, 
where it is replaced by a broken quartzite mixed with frag- 
ments of slaty material. This character is maintained for an- 
other 64 feet (or to a point 124 feet from the mouth) where a 
heavy-bedded flaggy slate is met on the hanging-wall, dip- 
ping 40° — S. 35° W. No porphyry, however, is visible. On 
the foot-wall is the " brecciated " slate, with fragments of 
quartz, some of it banded. Between this and the spot just re- 
ferred to were two places some 50 feet apart, where brecciated 
slates and quartz formed the principal part of the rock. At 
the heading of the Hoodoo tunnel, 359 feet from the mouth, 
occurs a fragmental quartzite following more or less the plane 
of bedding of the slates. According to report, the quartzite 
mass here is a]>out 40 feet below the lower surface of the por- 



12 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

phyry outflow. This under surface must, therefore, cut the 
tunnel at 60 feet fi-om its mouth, and its slope would be 1 foot 
in 7 or 8 to the south. 

The upper Hoodoo tunnel is about 15 feet higher in level 
than the main tunnel, and is all in porphyry. If this be the 
main body of porphyry and possess an even under-surface, it 
would make the slope more nearly 1 in 2, and imply a dip of 
30° from the mouth of this tunnel to the intersection of the 
porphyi'y and the main tunnel. 

In the cross-cut from its junction with the main drift for 63 
feet, the rock is fragmental quartzite interspersed with schists 
and shales ; but at this point the porphyry appears and con- 
tinues to the heading. 

Assuming the floor of the upper tunnel to be fifteen feet 
higher than that of the main tunnel and the distance 150 feet 
to the intersection of the porphyry and the cross-cut, the fall of 
the latter would be 1 in 10, corresponding to an angle of about 
60°. If these two bodies of porphyry are connected, as is 
practically certain, the facts would indicate that the strike of 
this sheet of porphyry is N.W. and S.E., and that the hill west 
of Strawberry creek and the Union Hill proper are on the same 
porphyry dike. 

This hill is distant from the shaft-mouth about quarter of a 
mile, on the west side of Strawberry gulch. The surface of the 
hill shows the same decomposed porphyry as Union Hill, above 
described, and the shallow openings, wherever made, bear out 
these indications ; but it is not certain how thick this cap of 
porphyry may be. On the summit of the hill and about quarter 
of a mile in a direct line from the Union Hill shaft is a cut in de- 
composed porphyry 30 feet long, 17 feet deep and 2i feet wide, 
in the bottom of which a nearly vertical vein widens to 2 feet 
from 8 inches at the surface. Small crystals of galenite are said 
to have been found in this vein. It is also reported that galenite 
has been taken from a dark ferruginous gangue. 

Near by is a shaft 126 feet deep. At the deepest point, an 
iron-ore is said to have been found, of which specimens were 
seen on the dump-pile. On both sides of the shaft appears a 
vein, which, at the depth of 100 feet, is said to have been 5 feet 
wide. 

A very instructive and interesting phenomenon, of a dike of 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 13 

porphyry cutting porphyry, was observed near the cut on top 
of this hill. It has a nearly vertical dip and a strike of N. 35 
W. 

If this observation be correct, it proves that there were suc- 
cessive outflows of porphyry at different epochs, and it may 
well be that one of these (not improbably the later) was more 
barren of the precious metals than the original outflow. At 
least a difterence in age would confirm the hypothesis that there 
are different kinds of dikes in this region, some of them aurif- 
erous and some of them entirely barren. One of the latter is 
seen on top of the hill near the Cora mine, S.W. of Galena. 

The assays of the specimens taken were as follows : 



Description. 



Surface of Union Hill. 



Average ore, experimental pit, 700 feet E. 

by S. of U. H. shaft 

Do., experimental pit S. of U. H. shaft... 
Do., deep cut, 165 feet N.W. of mouth of 

Hoodoo tunnel , 

Do., deep cut 

Shaft, Union Hill, "Horse," first level, 

heading S.E. drift 

Do., first level, heading S.E. drift 

Do., first level, heading N.W. drift 

Upper Hoodoo tunnel 

Main Hoodoo tunnel 



Total gold and silver in 12 tons of sample 



Average per ton. 



Dollars per Ton. 



Gold. Silver. 



0.4134 
0.8268 
0.4134 

Traces. 



11.57 
3.7206 

0.4134 
0.4134 
0.4134 
0.4134 
3.5139 



0.096 
0.096 



0.228 
0.480 



0.096 
0.072 
0.070 
0.192 



Total 
Dollars 
per Ton. 



0.4134 
0.9228 
0.5094 



11.7980 
4.2006 

0.4134 
0.5094 
0.4854 
0.4554 
3.7059 



$23.41 



$1.95 



Two samples collected by Mr. David Jones in the Hoodoo 
tunnel last October and assayed by different persons gave 
$43.70 and $4 per ton respectively. 

Messrs. Merrill and Sandt collected two samples of ore from 
Union Hill last September which gave $8.56 and $4.70 per ton, 
respectively, or a mean of $6.63. 

No sample of ore collected in the field can give as just a view 
of the real value of an ore-property as the results of a mill-run ; 
and I am therefore much indebted to the courtesy of Captain 



14 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

Boyd and the officers of the company in permitting me to use 
the following data obtained from a mill-run undertaken last 
October. This mill-run, as he explains, was of Union Hill ore, 
but was made during unusually cold weather, which froze the 
water on the plates in spite of all precautions. Despite these 
unfavorable conditions, he obtained $117 in gold from 40 tons 
of ore, which gives a value of $2.92 per ton. (He estimates 
that the unfavorable conditions of the run resulted in a loss of 
nearly two-thirds of the gold or $5, which would make the 
value of the ore treated $8 per ton, exclusive of the value of the 
concentrates, which he thinks will represent 1 to 80 in the por- 
phyry ore of Union Hill, and 1 to 5 in the ore of the Hoodoo 
tunnel.) 

The available quantity of the Union Hill ore depends upon 
the proportion which the porphyry of the hill bears to the 
country-rock above water-level. What we know about the hill 
is that its outer shell is composed of porphyry, and a part of its 
inner nucleus of the quartzites and shales, through which the! 
former has forced its way. Various views have been held in; 
regard to the geological epoch and the manner in which theses 
outflows took place. 

Numerous evidences of flow along the bedding and between 
the strata, as well as through rifts made by the upheaval of the 
measures, may be found in this part of the Black Hills. A 
similar rock in Wales has been thought by eminent geologists 
to be the result of volcanic outburst through several separated 
vents followed by a shower of ashes, which latter were later 
compacted into felsitic beds, which in course of consolidation 
become porphyritic. It is quite probable that there have been 
many such vents in this region, though several of them proba- 
bly united in the production of a single sheet of molten rock. 

Various observations tend to support the view that the por- 
phyry of Union Hill strikes N.W. and S.E., and may have been 
derived either from an outflow through a fracture in that direc- 
tion (since this does not correspond with the strike of the 
Archean schists) or from a series of vents, produced between 
the planes of the schist at different horizons, which united 
their outflows into one sheet. 

The broken and fragmental character of the rock in parts of 
the Hoodoo main and branch tunnels would indicate the close 



NOTES ON THE NORTHERN BLACK HILLS OP SOUTH DAKOTA. 15 

proximity of the cause of disturbance, even if the actual inter- 
section of both these drifts by porphyry were not observed. On 
the other hand, the continuance of porphyry (as I am reliably 
informed) throughout the 300 feet of the shaft, indicates either 
that the shaft has accidentally been located in a vent, or that the 
whole covering of porphyry is prodigiously thick. The former 
geems the more probable supposition, because, at a short dis- 
tance from the shaft, a large mass of quartzite may be seen' 
embedded in the igneous rock, and apparently at a considera- 
ble distance from any quartzite in place, as if it had been car- 
ried bodily upward in the igneous flow. 

The specific gravity of an average specimen of the porphyry 
was found to be 2.755. A cubic foot of this rock would thus 
weigh 171.64 pounds, and a cubic yard about 2i tons. The 
distance on the Union Hill property from the line of Strawberry 
gulch and its small eastern branch to the nnnith of the Hoodoo 
tunnel is about 2418 feet. Assuming a width of 1050 feet, 
which would include a large part of the company's property, 
and 256 feet, as the surveyor's estimate of the vertical depth 
of the mouth of the Hoodoo tunnel below the shaft-house, we 
have 619,008,000 cubic feet. Taking half of this amount, or 
309,504,000 cubic feet, as the cubic contents of the hill, and 
half of these contents, or 154,752,000 cubic feet, as consisting 
of porphyry, there would then be 26,617,344,000 pounds, or 
13,308,672 tons of porphyry above water-level. Assuming the 
average value of $1.95 per ton which resulted from the assays 
of ore which I selected, this would represent $25,951,910. 
Assuming the value actually obtained by Captain Boyd's mill- 
run of 40 tons (and without allowing for the loss which he 
believes to have taken place) or $2.92 per ton, the contents of 
the Union Hill would be valued at $38,861,322. 

I add a table, which, from a professional point of view, must 
be regarded as a curiosity. It represents assays of twelve sam- 
ples of carefully averaged ore made by three assayers of high 
reputation. There is no doubt whatever that the material of 
each of these triplicate assays was in a metallurgical sense the 
same. 

For the purpose of getting a better insight into the true char- 
acter of these porphyries, several specimens collected at difl'erent 
parts of Union hill were subjected to examinations under the 



16 NOTES ON THE NORTHERN BLACK 

Union Hill Ores, near 



HILLS OF SOUTH DAKOTA. 

Galena, S. D. 



Mark. 


Assayers. 


Gold. 


Silver, 


Total Value 

of Gold and 

Silver. 


Ounces per 

Ton of 2000 

Pounds. 


Value, 
820.67 per 
Ounce. 


Ounces per 

Ton of 2000 

Pounds. 


Value, 60 

Cents per 

Ounce. 


1 


A. 
B. 
C. 


0.100 
0.300 
0.230 


$2,067 
6.200 
4.754 


"2.35 




$2,067 
6.200 
6.15 




$1.41 


2 


A. 
B. 
C. 


0.08 
0.15 
0.08 


11.6536 
3.10 
1.6536 


"i'M' 




$1.65 
3.10 
2.30 




$0.64 


3 


A. 
B. 
C. 


0.10 
0.20 
0.13 


$2,067 
4.130 
2.68 


"6.89 




$2,067 
4.130 
3.21 


'$6.53 


4 


A. 
B. 

C. 


0.06 
0.25 
0.14 


$1.2402 
5.1700 
2.8900 


"6a6 




$1.24 
5.17 
3.15 




$0,276 


5 


A. 
B. 

C. 


0.08 

0.125 

0.08 


$1.6536 
2.58 
1.6536 


'0.96" 




$1.6536 

2.58 
2.1936 




$0.54 


6 


A. 
B. 

C. 


0.06 

0.125 

0.14 


$1.2402 

2.58 
2.89 


"0.31" 




$1.2402 
2.58 
3.37 




$0,486 


7 


A. 
B. 

C. 


0.04 

0.125 

0.04 


$0.8263 
2.58 
0.80 


"o.se" 




$0.8268 
2.58 
1.01 




$6,216 


8 


A. 
B. 
0. 






0.31" 






0.125 
0.03 


$2.58 
0.6201 




$2.58 
0.8061 


$0.1860 


9 


A. 
B. 

C. 


0.02 

0.125 

0.05 


$0.4134 

2.58 
1.035 


o.is' 




$0.4134 

2.58 
1.18 


$6." 150 


10 


A. 
B. 

C. 






0.26' 






0.1 

0.08 


$2.06 
1.65 




$2.06 
1.77 


$0.12 


11 


A. 
B. 
C. 


0.04 

0.075 

0.04 


$0.8268 
1.55 
0.8268 


'0.40' 




$0.8268 
1.55 
1.06 




$0.24 


12 


A. 
B. 
C. 


0.040 
0.200 
0.07 


$0.8268 
4.13 
1.4469 


■0.37" 




$0.8268 
4.13 
1.67 






$0,224 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 17 

Uyiion Hill Ores, near Galena, S. D. — Continued, 





Assayers. 


Gold. 


Silver. 


Total Value 

of Gold and 

Silver. 


Value, 
120.67 per 
Ounce. 


Value, 60 

Cents per 

Ounce. 


Average. 


A. 
B. 
C. 


$1.0676 
3.27 
1.9083 




$1.0676 
3.27 
2.3233 




$0.4181 



microscope as coarse powder and as thin slides in polarized 
light. Three specimens of this coarse pov^der were also kindly 
examined by Dr. Edgar F, Smith of the University of Pennsyl- 
vania, in his laboratory, for their percentage of alkalies and of 
silica. 



MkroscoiAcal Examination of the Concentrates From the Forphyry 
of Union Hill. 

It was an interesting question, in connection with this free- 
milling rock, in what state the gold occurred, whether free or 
attached to the pyrite or other minerals. The condition of the 
silver, which the assays proved to exist in eight or ten times 
larger quantity than the gold, was also very interesting. 

An experienced assayer reported the existence of " concen- 
trates with the appearance of pyrites largely mixed with hard 
particles of hematite, which was probably derived from the de- 
composition of the pyrites, A few colors of gold were visible 
which have a good yellow color In all of the sam- 
ples the relation of gold and silver fluctuates with some regu- 
larity." , . . , 

(L), — An examination of a quantity of concentrates under a 
magnification of about 100 diameters revealed gold in the free 
state and of a good yellow color (showing it unalloyed with 
silver), but in almost every case attached to a pyrite fragment. 

In several instances the association was as a lining to a little 
cavity, or in a crack of the pyrite, difiering from it in color 
and luster and apparently uncontaminated by combination 
with any other substance. 

Of the other metallic minerals present in the concentrates, 
pyrite and hematite and some limonite (named in the order of 



18 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

their quantity) formed perliaps 00 }»er cent. Besides these 
there were numerous non-metalHc mineral fragments, both of 
original and of secondary character, which were very interest- 
ing and unexpected. It should l)e remembered that the greater 
number of the specimens of porphyry from which the concen- 
trates were obtained came from points on or near surfaces 
which had been exposed to moisture and air for a considerable 
time, and therefore cannot be su[»[)Oscd to represent with cer- 
tainty the character of the interior mass of the porphyry. 

Following roughly the order of their frequency, the mmiTuls 
were orthoclase (both pegmatolite and sanidine), pyroxene, and 
a yellow silicate (?), the nature of which was not determined 
with certainty, but which is not suspected of being either i-are 
or important. It may be serpentine. 

A second examination of this concentrate follows. 

A comparatively large amount of the porphyry was con- 
centrated by panning, and examined under magnifying powers 
of 60 and 120 diameters, and proved to contain pyrite, quartz, 
rounded milky grains of feldspar, also reddish translucent 
grains with occasional circular groups on a surface exhibit- 
ing high refracting power, and resembling pegmatolite. Oc- 
casionally these two appearances are exhibited by the same 
grain. Translucent and generally rounded grains showing 
pale bluish or bluish green color and opalescence in transmitted 
light were observed ; also yellowish, barely translucent grains, 
and a minute mass of the finest hair-gold interwoven into little 
knobs, and spongy in appearance. 

There were also fragments of a dark bluish black mineral 
with metallic lustre and perfect cleavage on at least one plane 
(galenite) and argentite(?), diopside, beryl (one fragment), and 
cassiterite(? ?). 

Dr. Amos P. Brown, of the University of Pennsylvania, gives 
as his description of this powder (1) magnetite, (2) pyrrliotite, 
(3) pyrite, (4) chalcopyrite, (5) beryl, (6) serpentine(? — the yellow 
material alluded to above), (7) cassiterite(? ?) (8) quartz in small 
amount. 

(9. V. 21). — Another specimen was concentrated, and gave 
the writer pyrite, quartz, pegmatolite, yellowish translucent sili- 
cate, native gold, and galenite. 

Dr. Brown says of this : " It seems to have the same con- 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 19 

stituents as (L), but with a large percentage of the magnetic 
portion, which is mainly pyrrhotite, it would seem." He adds : 
"As I have no data as to the method of separation of their con- 
centrates, I do not know anything of the specific gravity, and 
can hence form but a poor guess of the constituents. The dark 
minerals are not in crystals, so the color and lustre only can be 
used in determination." 

A mass of this same powder which had not been concen- 
trated was given to Dr. Edgar F, Smith, from whom I have the 
following partial determination : 

Per cent. 

Si02, 63.53 

AI2O3 and Fe203, 22.89 

KzOandNaP, 7.35 

CaO, . 2.80 

MgO, not determined 

Undetermined, . 3.63 

100.00 

The rock is therefore a rhyolite with numerous mineral in- 
clusions, including native gold and combined silver, some of 
which are, in all probability, of secondary origin, and a few of 
wliich may have been transported from other places, inasmuch 
as all the specimens were taken at no great distance from the 
surface, and the rock was very generally broken and weathered. 

An analysis of this rock was made by Mr. V. Lenher in the 
John Harrison laboratory of chemistry of the University of 
Penn ylvania. It proved to be composed of: 

Per cent. 

SiO,, 61.79 

AI2O3, 17.79 

FeA 4.01 

CaO, 0.80 

MgO, 0.23 

K2O, 4.78 

NaaO, 7.56 

Loss on ignition, . . . . . . . . .3.46 

100.42 

This rock resembles in most of the constituents, except the 
silica and alkalies, a trachyte from Ischia near Naples ; but in 
those latter percentages is nearer to an acmite-trachyte from 
the Crazy mountains, Montana ; both cited by Prof Kemp. 

(1. V. 9). — The examination of this rock in coarse powder 
gave much the same results as that of the last, except that the 



20 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

grains, though smaller, were less translucent, and no free gold 
was observed. 

Dr. Brown describes it as containing " (1) magnetite, (2) pyr- 
rhotite, (3) pyrite, (4) diopside ( ? small amount), (5) quartz and 
flint. The same dark mineral as in (L) may be (6) cassiterite. 
(7) Some globular and botryoidal grains closely resemble some 
forms of cassiterite (or uraninite). There is also a little red 
opal. Possibly (7) may be limonite or psilomelane, but it is 
rather black." An analysis of this rock unconcentrated, made 
by Mr. George William Sargent, in the Harrison chemical 
laboratory of the University of Pennsylvania, yielded the fol- 
lowing results : 

Per cent. 

SiO^, 51.93 

AlA and Fe,A 31.35 

NaA 2.89 

KA 6.275 

CaO, 0.75 

MgO, 0.51 

Loss from ignition, . . . . . . . .7.26 

Total, 100.965 



The silica in the specimen is very low, and the alumina and 
iron sesqui-oxide are very high ; yet its position with reference 
to other more normal specimens leaves no doubt that it is part 
of the same outflow, modified, no doubt, by weathering. 

(E). — This porphyry was obtained from a shallow^ pit about 
900 feet E. of S. of the shaft-house on Union hill, and but a 
short distance above the main Hoodoo tunnel. 

It yielded to the examination of its concentrated powder very 
much the same results as those above. Quartz and feldspar 
predominated, and the pyrite was smaller in amount. The 
quantity of this concentrate was less than the others, though 
made from an equal quantity of powder. A small fragment of 
hematite was observed. 

Dr. Brown says of it: " Much like (10 V. 22), a large part of 
the magnetic part seems to be pyrrhotite. Quartz, barite(?), 
not much pyrite ; much black mineral, which looks like rutile 
or cassiterite."* 

* A considerable quantity of this powder was examined for me by Dr. S. P. 
Sadtler for the presence of tin, with negative results. The existence of cassiterite 
in this rock must therefore be considered as yet unproven. 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 21 

The unconcentrated powder of this rock was subjected to a 
partial analysis under the direction of Dr. Smith, with the fol- 
lowing results : 

Per cent. 

SiOa, 66.41 

AlA and Fefi^, 18.63 

CaO, 2.50 

Undetermined, 12.46 

100.00 

A specimen of the unground rock from this pit was cut and 
mounted in thin slides for examination by the polarizing mi- 
croscope. 

Under 60 and 120 diameters it proved to consist of a fine 
granular and hyaline matrix, including a considerable amount 
of quartz and secondary quartz, in which were imbedded large 
crystals of some sanidine and pegmatolite. A small amount of 
mica was also suspected. 

In another specimen the sanidine showed considerable corro- 
sion of the edges, and the matrix was of a texture suggesting 
the presence of silica deposited from solution. 

This rock is also a rhyolite, less rich, or perhaps entirely des- 
titute of valuable metallic constituents. 

Dr. Brown describes this section thus : " Sanidine in por- 
phyritic crystals, some micro-pegmatitic. Grains of primary 
quartz and much secondary quartz. This rock had apparently 
a glassy matrix originally. I do not find muscovite." 

In a later note he says : " It is a rhyolite without doubt. I 
should say it had originally a rather glassy base, but this had 
become devitrified. It is not apparently a very acid rhyolite, 
however." 

An analysis by Mr. V. Lenher in the John Harrison labora- 
tory of chemistry of the University of Pennsylvania demon- 
strated : 

Per cent. 

SiOi,, . 67.10 

AlA- 13.95 

FeA. 2.72 

CaO, 1.54 

MgO, 0.59 

K,0, 8.31 

Na^O, 2.43 

Loss on ignition, ......... 3.85 

100.49 



22 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

From its silica, alumina, iron sesqui-oxide, lime and mag- 
nesia, this rock resembles one from Flagstaff, Colo. ; and in 
the alkalies a rhyolite from Silver Cliif, Colo., of which 
analyses are published in the Handbook of Rocks. 

(10 V. 22). — The appearance under the microscope of the 
concentrated powder resembles very much that of (9. V. 21), 
l)ut it contained less pyrite, and no gold was observed. 

Dr. Brown's description is as follows : " (1) Magnetite, (2) 
pyrrhotite, (3) quartz, (4) pyrite, (5) same material as (7) in 
(1. V. 9), (6) also some of the dark mineral of (L. 7), and yel- 
low of (L. 6), perhaps serpentine. Much quartz, and a larger 
proportion of pyrrhotite than in the others." 

An unconcentrated specimen of this rock was analyzed in 
the laboratory of the University of Pennsylvania by Mr. George 
William Sargent, and gave the following results : 

Per cent. 

SiO^, 58.71 

AI2O3 and Fe.p3, 25.65 

Na^O, 3.61 

K2O, 6.69 

MgO, trace. 

CaO, 0.29 

MnO, 0.73 

Loss from ignition, 4.20 

Total, 99.88 

The silica is still rather low for a rhyolite, which, neverthe- 
less, we must suppose this to have been in its original state. 

A specimen of a coarse-grained rock {a) obtained from a point 
near the Union hill shaft on the surface of the hill, when cut 
into thin slides and examined under the microscope, exhibited 
a iine-grained matrix, in which rested short, thick slabs of lab- 
radorite and large prisms with pyramidal terminations of much 
disintegrated augite. Besides these, are some crystals of biotite, 
also small grains of some undetermined silicates and a little 
secondary quartz. The peculiar fragmentary condition of the 
pyroxene is striking. It is as if in pseudomorphs, or what ap- 
pear to be such, though the original form may have been py- 
roxene. 

Much of the granular matrix, associated with the usual acces- 
sory minerals accompanying angite or labradorite, is made up 
of small augite fragments. 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 23 

This rock seems to l)e an augite-aiidesite. 

Dr. Brown says of the sections of this rock : " It contains 
phigiochise, a little sanidine, augite (light-colored), and in a? 
(one of the slides) a little hrown hornhlende. Very little if 
any secondary quartz, augite-andesite." 

He adds in a subsequent note : " I think this could be safely 
called a pyroxene-andesite or augite-andesite, although I am of 
the opinion that some of the pyroxene may have been rhombic. 
' Pyroxene-andesite ' would be safe." 

The Coletta Group. 

The Coletta group of mines lies nearly due east of the Black 
Prince, 1^ miles down the valley of the Bear Butte creek. The 
openings are situated on the top of a steep hill which separates 
Spring run from Bear Butte creek, and at an average of 300 
feet above the beds of the streams. The rock is a quartzite, 
reported by Capt. Boyd to be here 175 feet thick and over- 
lying the Archean schists, which are nearly vertical. The dip 
is accordingly slight, about 5° — E. by S., and the ore con- 
forms to this dip, but occurs in a Y>eculiar form, called by Capt. 
Boyd " corrugations " or " corrugates." From whatever cause, 
there have been deposited on the upper surface of the quartzite 
uneven lenticular masses of ore like sausages strung together by 
slender strings, and dipping longitudinally towards the east. 
They lie approximately in the same plane at intervals of 30 to 
40 feet, parallel with each other, and are intersected by other 
similar masses at right angles, which increase both the richness 
and quantity of the ore at their junction. 

The cause of this strange phenomenon has been thought to 
be furrows or troughs made in the surface of the quartzite in 
which the metalliferous solutions deposited their contents ; but 
the origin of the depressions, and especially of these gridiron- 
like forms, is not clear. The length to which they continue is 
not known, the exploitation being terminated in most instances 
by the contour of the hill. 

Measurements of these corrugations show that they are 
broad and shallow lenticular masses, from 5 to 12 feet wide and 
from 8 inches to 3 feet thick. Where these lens-shaped masses 
are united end to end, or at the parts analogous to the connect- 
ing-string of the sausages, the rock becomes sandy, and free 



24 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

gold is found. The mineral matter consists mainly of carbonates 
of lead containing 50 cents to $12 per ton in silver and 0.2 ounce 
to IJ ounces of gold to the ton, and varying between 1 and 40 
per cent, of lead. These masses are said to increase in value 
with depth, which is natural from the manner of their deposit; 
the heavier and richer metals and their compounds having 
drifted to the lower planes. 

They are all more or less ferruginous, and siderite and mag- 
netite are reported to have been found in them. 

The ore exposed is a carbonate of lead containing nodules 
of cerussite. 

Tunnel No. 1, overlooking the valley and the hamlet called 
Virginia City, was opened on the nose of the hill by Mr. Harris 
in 1891, in a small shaft or pit sunk by an earlier prospector. 

The first pipe, encountered about 4 feet' from the tunnel- 
mouth and drifted on, was 1 foot wide, and increased shortly, to 
4 feet. The tunnel runs about S. by E., and the drift about E. 
The greatest thickness of these corrugations was 4 feet, and 
their greatest width 20 feet. Here the dip of the rock was 
5° — E. by S. in a decomposed quartzite. About 150 feet from 
the mouth of the drift it turns and is run on the small pipe. 
There are other horizons in the quartzite where the lenticular 
and gridiron-structure occurs, and pipes of ore connect them. 

A number of these tunnels are opened along the northern 
and eastern face of the hill at not very different levels. 

On the eastern face of the hill, in opening No. 5, the plane of 
the pipes has a strike of about S. 35° W"., and the pipes them- 
selves dip about 15°— E. 35° S. 

Samples from all the tunnels, Nos. 1 to 5, were taken and 
averaged, the product being indicated by the letter J below. 

A nodule of bright red color was selected from No. 5 and 
assayed. Vanadinite was found in parts of the face, and es- 
pecially in small crevices. Specimens were taken from open- 
ing No. 4 for examination. At the mouth of No. 5 a pipe 18 
inches thick, of yellow color, and containing heavy lead car- 
bonates, was observed. A short distance into the tunnel a flat 
lenticular mass or pipe, 10 feet wide and of unknown length, 
runs into the hill at an angle of about 15° — N. 35° W. Some 
30 feet south is another twin pipe or corrugation connected 
with it. This last has a breadth of about 4 feet where observed. 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 25 

About 100 feet S.W. from No. 5 is another opening, No. 6, 
into another pipe. Little was found outside these openings as 
dump, which is indirect testimony favorable to the character of 
the material excavated. 

At 100 feet E. of opening No. 6, and 25 feet lower, a large 
cavern or stope has been excavated under the lower edge of 
the quartzite, where a quantity of kaolin appears, and a con- 
siderable quantity of ore. The horizon is thought by Capt. 
Boyd to be the lower edge of the Potsdam, and it is not un- 
likely that it marks at least the lower edge of a lower Pots- 
dam quartzite. A banded quartzite called "ribbon-quartz" 
runs through the Archean schists at many localities in this 
country, which is said to be usually gold-bearing. 

At the Lynn, or No. 7, cut, 250 feet from the mouth and at the 
heading, a series of pipes was found with carbonates of lead 
averaging from 170 to 500 ounces of silver. This ore was 
sacked. (About 30 sacks make a ton.) Four tons or more 
have been taken from tins hole. Specimens taken from both 
sides of this drift were averaged and sampled, and the resultant 
specimen, labeled L, under which its assay will be seen below. 
(Vanadinite was also found here.) 

The mouth of the Lynn, or No. 7, tunnel is about 300 feet 
above water-level, and the extreme summit of the hill (which 
lies about S.E. of tunnel No. 1, and a little north of west of 
the Lynn tunnel) is about 50 feet above it, but Capt. Boyd es- 
timates the average cover of the mines at about 20 feet. 

Li general, it may be remarked that in tunnel No. 1 and the 
openings nearest to it, the pipes or corrugations are in rotten 
disintegrated rock ; but to the southeastward the quartzite in 
which the pipes are found becomes harder and firmer. 

About 300 feet S. 25° E. of this Lynn, or No. 7, tunnel, is 
another trial-shaft which showed some ore. At a depth of 
about 8 feet, at the bottom of the shaft a pipe is found strik- 
ing N. 25° W. and S. 25° E., but the ore is under such light 
cover that a great deal of it has been disseminated among the 
clays. 

According to Mr. Lynn, the surface indications of a pipe are 
a red soil and float-ore. 

The nearest Archean schists underlying tliis quartzite which 
were observed, dipped S. 35° E. — 85°. 



26 NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 

The assays of the specimens taken from the Coletta workings 
here follow : 

Assays from Coletta Workings. 













Dollars, gold, 












silver and lead 












per ton. 






Dollars 


per ton. 


Lead. 


(Lead at 


ark. 


Description. 


Gold. 


Silver. 


p.c. 


3.25 c. per lb.) 


J 


Tunnels 1 to 5, 


. 7.4412 


1.008 


5.6 


12.0892 


Ja 


Bright vermilion 












nodule in No. 5, 


. 29.3514 


10.068 




39.4194 


K 


Tunnel No. 5, . 


. 0.4134 


0.096 


11.17 


7.7694 


L 


Lynn or No. 7 tunnel, 


2.067 


27.408 


3.67 


31.845 



The lack of continuity in the ore-sheet caused by the breaks 
in the spaces between the gridiron of ore-bodies does not pre- 
vent a reliable estimate of the amount of ore from being made, 
for these corrugations persist with remarkable regularity. It 
was not easy to make a test of the amount of free-milling gold 
which occurs at the points where the ore-bodies pinch out, but 
it is likely to prove a large addition to the value of the ore here 
given. The lead is a valuable associate, and facilitates greatly 
the treatment in the smelter. With improved means of trans- 
portation to the Galena plant, whicli has already been projec- 
ted, a large, steady and profitable output Jiiay be confidently 
relied on. 

In the upper part of Galena, near the angle of Bear Butte 
creek referred to, the Archean schists dip S. 30° E. — 50°. The 
exposures show the rock in the hill to be compact, and in places 
curved and foliated. At this place a contact with porphyry is 
not far ofi[; in fact nature seems to have arranged the greatest 
possible number of contacts in this entire region, and to have 
prepared each contact with its quota of ores. The realization 
of this fact will explain the great prevalence of the word " con- 
tact," which one hears constantly. 

At the tunnel in the Cora mine, previously referred to, the 
opening is at the bottom of a middle quartzite dipping about 
5° — S.E. At the upper tunnel, at the junction of the Ar- 
chean schists with this quartzite, is plainly shown the former 
group, a.pinkish mica schist dipping E. 20° S. — 38°. (This low 
dip is doubtless due to the sagging of the laminte exposed on 
the upper side of the hill). The quartzite lying immediately 
upon it dips E. 10° S.— 18°. 



NOTES ON THE NORTHERN BLACK HILLS OF SOUTH DAKOTA. 27 

Mr. Mall, an old and experienced miner, states that in gen- 
eral, the quartzite of this region is thought by the experienced 
miners to dip E. at a low angle, and the schists S.E. 

It has been mentioned tluit on top of the Cora hill is a cap- 
ping of porphjry destitute of valuable mineral contents. The 
cleavage-planes of this rock seem to conform to bed-planes of 
the quartzite and dip 60° — E. 10° S. 

At another opening on a contact of quartzite with the over- 
lying shales, a quantity of cherty-looking red oxide of iron is 
observable. Lamellar oxides of iron with conchoidal fracture 
and smooth surfaces follow this upper contact. It would be im- 
portant to know whether this merges into pyrite deeper and 
further into the mine, where it is less exposed to the weather. 

The Cora mine produced galenite, silver and gold. 

List of Papers on Economic and Structural (jreolof/i/ of Black 
Hills. 

I am indebted to ]\Ir, \Yalcott, the Director of the United 
States Geological Survey, for the following bibliography on the 
economical and structural geology of the Black Hills : 

Englenmnn. Report on the geolocical exploration from Fort Leavenworth to 
Bryan Pass made in connection with a survey of a road from Fort Riley to 
Bridger's Bass under Bryan. Rept. of Sa-'y of War, 1856. Appendix H, 
pp. 508. 

Meek and Hayden. (Some remarks on the geology of the Black Hills and por- 
tions of the surrounding country.) Phila. Acad. ScL, Proc, vol. x., pp. 41-49, 
map. 1 859. 

Winchell (N. H.). Reconnaissance of tlie Black Hills of Dakota, U. S. A. Rept. 
of Chief of Engineers, 1874. Appendix PP, vol. ii., part 2, pp. 1131-1172. 

Newton (Henry). Geology of the Black Hills. Introduction. Report on the 
Black Hills of Dakota, J. W. Powell in charge. Washington, 1880. 

Jenney (Walter P.). Mineral resources of the Black Hills of Dakota. Rept. on 
the Black Hills of Dakota, J. W. PoAvell in charge. Washington, 1880. 

Devereux Walter B.). The occurrence of gdld in the Potsdam formation, Black 
Hills, S. Dak. Trans. A. I. M. E., vol. x., 1882, pp. 465-475 (with section 
near Homestake). 

Newberry (J. S. ). The Deposition of Ores. School of Mines Quart., vol. v., p. 
336. 

Blake (Wm. P.). Tin-Ore Veins in the Black Hills of Dakota. Trans. A. I. 
M. E., vol. xiii., pp. 691-696. 1885. 

Chance (H. M.). Kesources of the Black Hills and Big Horn Country, W^yom- 
ing. T^ans. A. I. M. E., vol. xiv., p. 49. 

Carpenter (Franklin R. ). Notes on the Geology of the Black Hills. Preliminary 
Report of the Dakota School of Mines upon the Geology, Mineral Resources and 
Mills of the Black Hills of Dakota, pp. 11-52, map. 1888. 




28 NOTES ON THE NORTHERN BLACK HILLS OF SOUl 

016 094 164 9 i 

The Mineral Kesources of the Black Hills, their Character, Uccurrence, ana 

Extent. Preliminary Report of the Dakota School of Mines, etc., pp. 107-171. 

1888. 

Ore-deposits of tlie Black Hills of Dakota. Trans. A. I. M. E., vol. xvii., 

pp. 570-598. 1889. (With colored geological map). 
Crosby (W. O.). Geology of tlie Black Hills of Dakota. Bost. Soc. Nat. Hist., 

Proc, vol. xxiii., pp. 488-517 and vol. 24, p. 11. 1888. 
Van Hise, (C. B.). The Pre-Cambrian Eocks of the Black Hills. Ocol. Soc. Am., 

Bull., vol. i., pp. 203-244. 1890. 
Ward (Lester F. ). The Cretaceous Rim of the Black Hills. Jour, of Geol., vol. 

2, pp. 2.50-266. 
Posepny (F.). The Genesis of Ore-Deposits. Trans. A. I. M. E., vol xxiii,, pp. 

197-369. 
Todd (James E.). A Preliminary Report on the Geology of South Dakota. S. D. 

Geol. Surv., Bull. No. 1, pp. 172. 
Pirason (L. V.). On Some Phonolite Rocks from the Black Hills. Am. Jour. 

Sci., 3dser., vol. xlvii., pp. 341-346. 
Hall (Charles E.). A Vacation-Trip into the Black Hills of South Dakota. Ab- 
stract : Jfwm. Acad. Nut. Sci., Bull., vol. iii., pp. 185-186. 
Hall (W. S.) The Soutli Dakota Artesian Basin. Science, vol. xxii., pp. 20-30. 
Headden (Wm. P.). Stannite and its Alteration Products from the Black Hills, 

Soutli Dakota, uim. Jour. Sci.., Sd ser., vol. Ixv., pp. 105-110. 
Claypole, (E. W.). The Tin-Island of the Northwest. Am. Geol., vol. ix., pp. 

228-236. 
Ulke (Titus). A New Tin-Mineral in the Black Hills. Trans. A. I. M. E., vol 

xxi., pp. 240-241. 

A Contribution to the Geology of the Dakota Tin-Mines. Encj. and Min. 

Jour., vol. liii., p. 547. 
Rolker (Charles M.) The Production of Tin in Various Parts of the World. 

U. S. Geol. Surv., 16th Ann. Rep. Part III., pp. 458-538. 
Todd (J. E.) Recent Geological Work in South Dakota. Am. Geol., vol. xvi., 

p. 202. 
Rickard (T. A.). Variations in the Milling of Gold-Ores.— Xll. The Black 

Hills, South Dakota. Emj. and Mg. Jour., vol. Ix., pp. 221-223 and 247-251. 
See also Bulletin No. 127, U. S. Geol. Surv., Catalogue and Index of Contributions 

to N. Amcr. GcoL, 1732-1891, by N. H. Darton, under the heading Dakota. 



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